Transcatheter procedures are rapidly replacing surgical procedures, such as coronary interventions for coronary artery bypass grafting (CABG), intravascular repair and stenting for vascular surgery, and catheter ablation of complex arrhythmias for arrhythmia surgery. Typically transcatheter approaches are done under fluoroscopy which uses ionizing radiation. Radiation exposure is of concern to the public and medical community. Medical imaging is a significant cause of manmade radiation exposure, hence many guidelines and appropriateness use of this procedure and imaging technology has been developed.
Medical treatment of patients with cardiovascular disease such as atherosclerosis, cardiac arrhythmias, aneurysms, often includes a medical professional performing angiography. Angiography comprises obtaining x-ray fluoroscopic imaging that involves guiding a catheter through femoral or carotid arteries (brain vascular interventions) with x-ray fluoroscopic image guidance, and frequent injection of iodinated contrast agent to visualize internal anatomy of the vasculature to evaluate blood flow, constrictions, or blockage, and plan an appropriate treatment. Traditional systems and methods for angiography can expose the patient, the angiography suite staff, and the physicians to significant doses of ionizing radiation.
X-ray angiography is considered the industry's typical imaging standard for the evaluation of cardiovascular anatomy within the body. The angiography procedure requires insertion of a catheter with guide wires through an artery or vein with frequent injection of contrast media, and use of x-ray fluoroscopy to guide the catheter to the area of interest. The x-ray angiography provides high resolution imaging showing vasculature anatomical details, left ventricular ejection fraction, and cardiac output. However, x-ray angiography still requires fluoroscopy, and can expose the patient, the angiography suite staff, and the physicians to significant doses of ionizing radiation.
Other methods, such as magnetic resonance angiography (MRA), computed tomography angiography (CTA), and 3D rotational angiography (3DRA) with contrast medium, are used to delineate the cardio-vascular system. While MRA has the advantage of using non-ionizing radio frequency (RF) energy, it does not provide by itself real-time guidance within the vasculature. CTA and 3DRA use ionizing radiation and an iodinated contrast agent, which again can expose the patient, the angiography suite staff, and the physicians to significant doses of ionizing radiation.
These methods have the risk of exposing patients and hospital personnel to ionizing radiation. The risk is substantial. There are risks of skin erythema, skin necrosis, malignancy, genetic abnormalities, and adverse reactions to iodinated contrast media including kidney shut down and death. Further, from the interventional cardiologist's perspective, fluoroscopy systems can also be problematic because the system is bulky and limits intra operative flexibility as well as free movement of angiography instruments.
Atrial fibrillation (AF) is the most common sustained arrhythmia of many etiologies. According to reports, there are about six to seven million Americans suffering from AF and it is predicted that by 2050 AF prevalence may reach 15 to 16 million. Approximately 35% of hospitalizations due to arrhythmias are from AF. AF costs Medicare more than 15.7 billion dollars annually.
Stroke is one of the most significant and devastating burdens of AF. Stroke affects 800,000 Americans annually—almost one every forty seconds. Stroke is the third leading cause of death and the number one cause of disability. Eighty-seven percent of strokes are ischemic, i.e., embolic, and the most common source is related by far by AF.
Anti-arrhythmic drugs are used in 90% of cases. However the success rate of these medications is less than 50%. More recent trials revealed negative outcomes of anti-arrhythmic therapy. Two of the most recent trials were prematurely terminated due to adverse effects of these drugs (Pallas; N Engl J Med 2011; 365:2268-2276, and Alphee trial; Kowey P R. Circulation; 2011; doi: 10. 1161/CIRCULATIONAHA. 111.072561).
Transcatheter ablation of AF is increasingly used to “cure the arrhythmia”. The procedure typically requires multiple catheter insertions and the use of radio frequency currents. High intensity focused ultrasound or cryoablation using a balloon are alternates having less success. The success rate of paroxysmal AF ablation with low co-morbidity is about 70-80%. In patients with advanced heart disease such as heart failure and persistent AF, the acute success rate of AF ablation is about 50-60% with a high recurrence rate at one year.
AF ablation using RF typically requires multiple site burns and is typically a lengthy procedure with high radiation exposure. A main reason for the low success rate is the anatomical complexity of the arrhythmogenic substrate and reconnection of isolated pulmonary veins to the left atrium. AF is an evolving disease and a moving target by itself. Successful AF ablation can depend on completely ablating target tissue without any gaps. The gaps are usually the cause of reconnection and recurrence of AF.
Ventricular tachyarrhythmias (VT) are another arrhythmia that often causes syncope (loss of consciousness) and cardiac arrest. It is estimated that about 350,000 to 450,000 cases of sudden cardiac deaths occur annually in the U.S. The majority of these cases are due to VT and ventricular fibrillation. So far the only effective method to abort and or prevent sudden cardiac death is implantation of cardioverter defibrillator devices known as ICD's. This procedure is costly and designed to terminate arrhythmias when it occurs. It does not however prevent nor cure as it does not eliminate or modify the arrhythmogenic substrate.
Traditional ablation catheters and electrodes have been used for transcatheter ablation of endocardial and/or epicardial arrhythmogenic tissue to treat VT. Traditional ablation catheters in these areas of the heart have limited success and a high recurrence rate. The possible cause of this is related to the complexity of the arrhythmogenic substrate and the mechanism of arrhythmia itself. Traditional ablation catheters and electrodes do not identify the characteristics of the arrhythmogenic substrate via direct visualization and monitoring while ablating, nor do they ablate uniformly without possible gaps.